Trade unions and political party leaders praised Sue Bradford and mourned her imminent departure after the Green Party MP announced today she was resigning from Parliament.
Ms Bradford recently lost a contest for the party's co-leadership and said it was time for a change.
Her decision, effective on October 30, was prompted by the leadership contest which she lost to Metiria Turei, after Jeanette Fitzsimons stood down, she said.
"The party made a clear and democratic decision, but of course it was personally disappointing and I'm ready for a change," a teary-eyed Ms Bradford said at a press conference today.
"It's been a tough four months ... and I have spent the time since then thinking very deeply about my future."
Council of Trade Unions president Helen Kelly said Ms Bradford would be "hugely missed" by the union movement.
"Sue is a true champion of working people," Ms Kelly said.
"She understands working people's concerns and, building on her years of activism, has campaigned tirelessly as an MP on many important social issues - including advocacy for beneficiaries."
Barnardos New Zealand said Ms Bradford's work in Parliament had been outstanding.
"Her imminent departure is a significant loss for the people she so effectively represented," said chief executive Murray Edridge.
Labour leader Phil Goff said Parliament was losing a strong and passionate advocate for low income workers, unemployed people, beneficiaries "and other people who might get a raw deal".
Mr Goff said Ms Bradford made a significant impact on Parliament during her decade as an MP.
"Her passion for the causes she fought for as an activist will be missed."
Maori Party co-leader Tariana Turia said Ms Bradford had an enormous commitment to improving the lives of families.
"I have greatly admired her courage and I know wherever she goes she leaves behind big footprints to follow," Mrs Turia said.
"The loss for the Greens will be huge."
Ms Bradford said she had decided a clean break was best as she did not want to become an MP "who is here, but their heart is not in it".
It had hurt to lose and she had been no good at hiding that, "but one of us had to lose".
Ms Bradford said she was not leaving because of any disagreement of policy or political direction.
"It is just better to leave rather than stay on and not be particularly happy."
Green Party co-leader Russel Norman said the party would have liked Ms Bradford to stay, but respected her decision.
The 57-year-old MP had spoken out for the vulnerable and for those who otherwise would have had no voice, Dr Norman said.
"We will miss her," he said.
Dr Norman said the Greens were now an established political force that would continue to see people come and go as it was an enduring political party.
Ms Bradford, a four-term MP, said she would remain a party member and active with community groups and unions.
"I'll always be politically active and Parliament is just one vehicle for political change. I'll be going back to the grassroots."
The Green Party's new MP will be Aucklander Dave Clendon, a sustainable business adviser.
Ms Bradford is a long-time political activist.
Her parliamentary career was dominated by her bill amending section 59 of the Crimes Act which removed the defence of reasonable force when an adult was charged with assaulting a child.
Its passage with the support of Labour and National had been the highlight of her career, she said.
"(The law change) marked a huge shift in this country and how this Parliament sees children," she said.
She praised Prime Minister John Key for refusing to repeal the law and believed it would be consolidated over time.
Asked if she had thought about staying in Parliament to defend her law, Ms Bradford replied:"If I waited for the section 59 issue to be resolved, I might be heard till I am 93."
Ms Bradford said her biggest regret was not becoming minister for social development and housing.
"My true ambition in coming here was to shake up and reform our welfare system and also to do a lot in the housing sector."
Ms Bradford was banned from Parliament before she became an MP because of her protests and she predicted a return to the other side of the barricades would not be far away.
